1. Technical Field
The invention relates to the art of tire inflation systems. More particularly, the invention relates to tire inflation systems for heavy-duty vehicles such as trucks and tractor-trailers or semi-trailers, which can operate as the vehicle is moving. Still more particularly, the invention is directed to a tire inflation system that is a constant pressure system which continuously balances pneumatic pressure across all of the tires in the system, and provides emergency protection in the event a tire in the system experiences significant pressure loss.
2. Background Art
Heavy-duty vehicles typically include trucks and tractor-trailers or semi-trailers. Tractor-trailers and semi-trailers, which shall collectively be referred to as tractor-trailers for the purpose of convenience, include at least one trailer, and sometimes two or three trailers, all of which are pulled by a single tractor. All heavy-duty vehicles that are trucks or tractor-trailers include multiple tires, each of which is inflated with a fluid or gas, such as air, to an optimum or recommended pressure. This optimum or recommended tire pressure typically is referred to in the art as the target inflation pressure or the target pressure.
However, it is well known that air may leak from a tire, usually in a gradual manner, but sometimes rapidly if there is a problem with the tire, such as a defect or a puncture caused by a road hazard. As a result, it is necessary to regularly check the air pressure in each tire to ensure that the tires are not significantly below the target pressure and thus under-inflated. Should an air check show that a tire is under-inflated, it is desirable to enable air to flow into the tire to return it to the target pressure. Likewise, it is well known that the air pressure in a tire may increase due to increases in ambient air temperature, so that it is also necessary to regularly check the air pressure in each tire to ensure that the tires are not greatly above the target pressure and thus over-inflated. Should an air check show that a tire is over-inflated, it is desirable to enable air to flow out of the tire to return it to the target pressure.
The large number of tires on any given heavy-duty vehicle setup makes it impractical to manually check and maintain the target pressure for each and every tire. This difficulty is compounded by the fact that trailers of tractor-trailers or trucks in a fleet may be located at a site for an extended period of time, during which the tire pressure might not be checked. Any one of these trailers or trucks might be placed into service at a moment's notice, leading to the possibility of operation with under-inflated or over-inflated tires. Such operation may increase the chance of less-than-optimum performance and/or reduced life of a tire in service as compared to operation with tires at the target pressure, or within an optimum range of the target pressure.
Moreover, should a tire encounter a condition as the vehicle travels over-the-road that causes the tire to become under-inflated, such as developing a leak from striking a road hazard, the life and/or performance of the tire may be significantly reduced if the under-inflation continues unabated as the vehicle continues to travel. Likewise, should a tire encounter a condition that causes it to become significantly over-inflated, such as increasing pressure from an increased ambient air temperature, the life and/or performance of the tire may be significantly reduced if the over-inflation continues unabated as the vehicle continues to travel. The potential for significantly reduced tire life typically increases in vehicles such as trucks or tractor-trailers that travel for long distances and/or extended periods of time under such less-than-optimum inflation conditions.
Such a need to maintain the target pressure in each tire, and the inconvenience to the vehicle operator having to manually check and maintain a proper tire pressure that is at or near the target pressure, led to the development of prior art tire inflation systems. In these prior art systems, an operator selects a target inflation pressure for the vehicle tires. The system then monitors the pressure in each tire and attempts to maintain the air pressure in each tire at or near the target pressure by inflating the tire when the monitored pressure drops below the target pressure. These prior art tire inflation systems inflate the tires by providing air from the air supply of the vehicle to the tires by using a variety of different components, arrangements, and/or methods. Certain prior art systems are also capable of deflation, and these systems deflate the tires when the monitored pressure rises above the target pressure by venting air from the tires to atmosphere.
While being satisfactory for their intended functions, tire inflation systems of the prior art may experience disadvantages in certain situations. For example, a first disadvantage in the prior art is that many prior art tire inflation systems are not capable of deflation. As a result, when the air pressure in a tire increases to a level that is greatly above the target pressure, typically due to increases in ambient air temperature, these systems are unable to reduce the pressure in the tires. As a result, such prior art tire inflation systems may allow the tires to operate in a significantly over-inflated condition, which undesirably decreases performance of the tires and in turn decreases the life of the tires.
A second disadvantage occurs in prior art tire inflation systems that are capable of deflation. More particularly, deflation-capable systems typically are electronically controlled, employing electronically-operated solenoid valves, electronic controllers, and other electronic components, which are expensive and are often complex to install and configure. In addition, these electrical components require the use of the electrical system of the vehicle, which may be unreliable or even non-functional at times, in turn rendering the operation of the tire inflation system unreliable and potentially non-functional. As a result, prior art deflation-capable tire inflation systems which are electronically controlled are often undesirably expensive, complex, and potentially undependable.
A third disadvantage is that most prior art tire inflation systems which are capable of deflation, and particularly electronically-controlled systems, are not constant-pressure systems and thus do not actively monitor tire pressure. More particularly, in the prior art, the principal goal of most deflation-capable tire inflation systems has been to respond to operator-controlled adjustments of the target inflation pressure, rather than to actively monitor tire pressure and continuously maintain the target inflation pressure. As a result, in most deflation-capable prior art tire inflation systems, when the system is not performing inflation or deflation, the pneumatic conduit of the system is exhausted to atmosphere.
In such a system, without air pressure in the pneumatic conduit, electronic controls are employed to periodically check tire pressure, and to in turn trigger or commence inflation or deflation, as may be required. Because such prior art systems are capable of only providing a periodic check of tire pressure, any inflation or deflation to bring the tires to the target pressure only takes place following the periodic check. This lack of ability of prior art systems to continuously monitor tire pressure and dynamically respond to pressure changes undesirably reduces the ability of the system to actively or quickly respond to reduced tire pressure conditions, such as in the case of an air leak, and to increased tire pressure conditions, such as an increase in ambient temperature. Moreover, as mentioned above, the electronic controls employed by prior art tire inflation systems are expensive, complex, and require power from the electrical system of the vehicle, which may be unreliable.
A fourth disadvantage of prior art tire inflation systems is that most systems, and particularly those prior art systems which are constant-pressure systems, do not provide balancing of pneumatic pressure across all of the tires in the system. More particularly, as described above, a typical heavy-duty vehicle includes multiple tires, and each one of those tires is operatively and independently connected to a single tire inflation system. More specifically, most prior art tire inflation systems are connected directly to each tire, and of these, many include a one-way check valve for each tire that prevents air from exiting the tire. In such a configuration, the tire inflation system monitors the pressure in each tire, inflating any tire that falls below the target pressure. While such separate inflation of each tire is satisfactory for its intended purpose, such prior art systems are not capable of deflation of the tires, and thus are unable to reduce the pressure in the tires when it increases to a level that is greatly above the target pressure.
In addition, such prior art systems lack fluid communication between the tires. Without fluid communication between the tires, different tires may be inflated to slightly different pressure levels, which is undesirable. More particularly, many heavy-duty vehicles include a dual-wheel or dual-tire configuration, in which two tires are mounted on a single wheel end assembly. Because the two tires are mechanically connected to each other through their respective mounting on the same wheel end assembly, they rotate at the same speed during vehicle operation. Although both wheels are designed to be the same diameter, their actual respective diameters are slightly different, since the lack of fluid communication between them causes them to be inflated to slightly different pressure levels. The difference in actual respective diameters between the tires, while they rotate at the same speed, causes one of the tires to experience dragging, which is also referred to in the art as scrubbing. Scrubbing of a tire causes premature wear on that tire, and undesirably shortens the life of the tire.
In addition, the lack of fluid communication between the tires undesirably increases the chance that a tire may operate with an excessively low inflation pressure. For example, in the event that one tire in the system is about fifty percent (50%) below the target inflation pressure, a prior art system may take a significant amount of time to bring the pressure in the low tire up to the target pressure. During that time, it is possible for the tire to be operated in a significantly under-inflated state, which decreases its life. In contrast, when there is fluid communication between the tires, each of the remaining tires in the system passes air to the tire that is below the target inflation pressure. Because multiple tires, such as seven or more tires, each pass a relatively small amount of air to the low-pressure tire, the low pressure tire receives air much more quickly, and all of the tires in the system balance at a pressure that is only slightly below the target pressure, such as about five percent (5%) below the target pressure. In the art, it is more desirable to operate the vehicle with multiple tires that are slightly below the target pressure until the system is able to bring them up to the target pressure, rather than operating the vehicle with a single tire that is significantly below the target pressure.
A fifth disadvantage of prior art tire inflation systems occurs in the few prior art systems which do provide balancing of pneumatic pressure across all of the tires. More specifically, in prior art tire inflation systems that do provide balancing of pneumatic pressure, all of the tires are in fluid communication with one another, and the tires thus have a generally uniform, or balanced, inflation pressure. However, these systems do not provide emergency protection of the tires in the event that one tire experiences a significant pressure loss. For example, if a specific tire is punctured or a pneumatic conduit at the tire ruptures, it is important to pneumatically isolate the system from that tire due to the fluid communication between the tires. In such a system, if the system is not isolated from a tire that is experiencing a significant pressure loss, the uniform inflation pressure of all of the tires may decrease significantly, which may place an excessive inflation demand on the system. The system may not be able to meet this demand, which may result in the tires being operated below the target inflation pressure, in turn reducing tire life, and/or the system may actuate excessively to attempt to meet the demand, thereby reducing the life of the system.
As a result, there is a need in the art for a tire inflation system that overcomes the disadvantages of the prior art by providing a constant-pressure tire inflation system that is capable of deflation, is not electronically controlled, balances pneumatic pressure across all of the tires in the system, and includes emergency protection of the tires in the event that one or more tires experiences a significant pressure loss. The constant pressure pneumatic balancing tire inflation system of the present invention satisfies this need, as will be described in detail below.